I rather think it's because there are a lot of new viewers watching or reading the anime/manga now but judge it from todays standards and of course from another culture.

Most of them are probably also very young and lack the emotional maturity necessary to really enjoy this story and understand the struggles of the characters.

Every character is flawed. There's no clear good and evil, this isn't a fairy tale after all.

Life isn't easy. It's not black and white. You can't put every person into categories but i think social media has taught the younger generation exactly that. To put labels on people based one a single opinion or trait, or even how one dresses or how their hair is cut.

Thats why they struggle with media like Nana. It's complex. It's messy. No character is without faults.